1. Field of the Invention
The present invention relates to a system for estimating a fault point in a semiconductor device such as a CMOS integrated device.
2. Description of the Related Art
In a first prior art system for estimating a semiconductor device, an electron beam tester is used to irradiate the semiconductor device with electrons, thus obtaining a potential contrast image from the semiconductor device. That is, potential contrast images for functional test patterns are stored and are compared with those of a non-defective semiconductor device. In this case, a determination of whether or not the device is defective is carried out by monitoring the output signals of the semiconductor device. If the semiconductor device is determined to be defective, the functional test patterns are retarded as decremental time sequences (see T. C. May et al., "Dynamic Fault Imaging of VLSI Random Logic Devices", IEEE/IRPS, pp.95-108, 1984).
In the first prior art system, however, unless the output signals of the semiconductor device are abnormal, it is impossible to substantially estimate a fault point in the semiconductor device. Also, comparison between potential contrast images of a tested semiconductor device and potential contrast images of a non-defective semiconductor device is required which increases the test time.
A second prior art system for estimating a fault point in a semiconductor device uses an optical emission microscope having a function for accumulating detected light (see: H. Ishizuka et al., "STUDY OF FAILURE ANALYSIS USING PHOTON SPECTRUM", REAJ 4-TH SYMPOSIUM, VoL. 13, No. 3, pp.71-76, November 1991).
In the second prior art system, however, if a fault point is beneath a conductive layer, it is impossible to detect light generated from such a fault point, since the light is reflected by the conductive layer. In addition, when a leakage current flowing through a fault point is so large as to remarkably increase the light intensity, it is impossible to normally operate the optical emission microscope.